The invention concerns an apparatus for promoting dissolution of gas into liquid by entraining gas from the liquid surface and dispersing it into the liquid body. A particularly useful application of the invention is in the aeration of wastewater for the aerobic treatment process. Up to date there are three principal methods used in activated sludge process: the submerged diffuser method, the submerged turbine method, and the surface aeration method.
In the first method, submerged diffusers are used. The gas phase is compressed and then introduced to the liquid near the bottom of the tank through a porous diffuser head. It is known that the efficiency is generally low. Besides, the cost of maintenance is high due to the clogging problem of the porous head. The second method is using a submerged turbine. The gas is compressed and let out through a conduit near the bottom of the tank. The submerged turbine is placed above the gas outlet. The rotating motion of the turbine produces kinetic energy and turbulence for dispersing and mixing the discharged gas with the liquid. With this method the absorption efficiency is higher and there is less clogging problem. However, it not only requires a gas compressor but also a rotating turbine and therefore the initial cost is high and there are more components to maintain.
The last method is known as surface aeration which utilizes a rotating body with vanes for spraying the liquid into droplets. The droplets contact with the gas phase while traveling in the air. Surface aeration is a very effective method and mechanically it is simple. However, there are many disadvantages such as inadequate local mixing, limitation in tank depth due to poor mixing and contamination of the atmosphere around the system.